1. Field of the Invention
The present invention relates to prevention or restriction of thermal deformation of a rotor tail end of a steam-cooled gas turbine.
2. Description of the Related Art
The temperature of the burnt gas at an inlet of a gas turbine has been increasing to increase the efficiency of the gas turbine, and in recent years, a gas turbine in which the temperature reaches 1500xc2x0 C. has been proposed.
A so-called steam-cooled gas turbine, in which the relatively low temperature of steam is used as a coolant, to protect stator blades and rotor blades of the gas turbine from the burnt gas of high temperature, in place of a conventional air cooling system, is being developed. To cool the rotor blades of the gas turbine by steam, it is necessary to provide steam passages for supplying and recovering the cooling steam for the rotor blades, along the center axis of the rotor of the gas turbine.
A rotor assembly of a gas turbine having a plurality of rotor disks which are fastened to each other by spindle bolts so as to rotate together is rotatably supported by a journal bearing. Since the rotor assembly of the gas turbine is very heavy, the gap between the shaft portion of the rotor assembly and the journal bearing is very precisely administrated. However, in the steam-cooled gas turbine, the steam passes through the center portion of the rotor assembly and, hence, the latter and in particularly its shaft portion is thermally deformed, so that the journal bearing can be damaged.
It is an object of the present invention to eliminate these problems, by providing a shaft structure and bearing structure, for a rotor tail end of a steam-cooled gas turbine, in which little or no thermal deformation of the rotor tail end of the gas turbine occurs.
According to an aspect of the present invention, there is provided a shaft structure of a rotor tail end of a gas turbine in which a steam passage for supplying and recovering a steam for cooling rotor blades of the gas turbine extends along a center axis of the rotor assembly of the gas turbine, wherein a center hole of the rotor tail end coaxial to the center axis of the steam passage is formed in the rotor tail end; a thermal sleeve is provided between the steam passage and the inner surface of the center hole of the rotor tail end; a thermal insulation gas layer is formed between the inner surface of the center hole of the rotor tail end and the thermal sleeve; and the thermal insulation gas layer is isolated gas-tightly and liquid-tightly from the outside.
According to this embodiment of the invention, a thermal sleeve is provided between the steam passage and the inner surface of the center hole of the rotor tail end, so that a thermal insulation gas layer is formed between the inner surface of the center hole and the thermal sleeve. Consequently, when the steam for cooling the turbine rotor blades passes in the steam passage, the heat transfer to the vicinity of the surface of the shaft portion is restricted, thus resulting in little or no thermal deformation of the shaft portion. Moreover, the thermal insulation gas layer is gas-tightly or liquid-tightly isolated from the outside, no steam enters the thermal insulation gas layer. Therefore, if the temperature drops during the stoppage of the gas turbine, no drain of the steam due to the condensation thereof occurs. Thus, no abnormal vibration due to the drain of the steam takes place.
The thermal sleeve can be in the form of a substantially circular cylinder which is welded at its one end to an end disk of the gas turbine and welded at the other end to a shaft portion of the rotor tail end. The thermal sleeve can be provided with a bent portion in the vicinity of the end thereof welded to the shaft portion of the rotor tail end. Consequently, if a temperature difference is caused between the thermal sleeve and the shaft portion, due to the steam passing in the steam passage, the bent portion absorbs the thermal expansion in the axial direction due to the temperature difference to thereby prevent the thermal sleeve from being damaged or broken.
When the thermal sleeve is welded to the end disk or the shaft portion, a pre-tension is preferably applied to the thermal sleeve. The welding of the pre-tensed thermal sleeve to the shaft portion prevents the occurrence of thermal deformation of the thermal sleeve. Moreover, the bent portion and the application of the pre-tension contributes, in combination, to further restriction of the thermal deformation of the thermal sleeve and to a prevention of the thermal sleeve from being damaged or broken.
In another embodiment of the invention, a shaft structure of a rotor tail end of a gas turbine in which a steam passage for supplying and recovering a steam for cooling rotor blades of the gas turbine extends along a center axis of the rotor assembly of the gas turbine, comprises a plurality of shaft portion cooling air passages formed between the steam passage and an outer surface of a shaft portion of the rotor tail end.
According to the embodiment, a plurality of the shaft portion cooling air passages are formed between the steam passage and the outer surface of the shaft portion of the rotor tail end, so that the cooling air passes in the shaft portion cooling air passages. Consequently, when the steam for cooling the turbine rotor blades passes in the steam passage, the shaft portion is cooled by the cooling air passing in the shaft portion cooling air passages, so that the thermal deformation of the shaft portion can be reduced or restricted.
The shaft portion cooling air passages are at least partly formed by directly drilling the shaft portion. Alternatively, the shaft portion can be comprised of a shaft body portion which surrounds the steam passage, and a sleeve fitted on an outer surface of the shaft body portion, so that the shaft portion cooling air passages can be formed at least partly between the shaft body portion and the sleeve.
According to another aspect of the present invention, there is provided a bearing structure for bearing a shaft portion of a rotor tail end of a gas turbine in which a steam passage for supplying and recovering a steam for cooling rotor blades of the gas turbine extends along a center axis of the rotor assembly of the gas turbine, comprising a bearing pad which forms a journal bearing, and seal portions provided on opposite sides of the bearing pad in the axial direction to prevent leakage of a lubricant for lubricating a space between the bearing pad and the shaft portion, the width of the seal portion in the axial direction being such that the surface temperature of the shaft portion of the rotor tail end is maintained below a predetermined temperature by the lubricant, within the width of the bearing pad in the axial direction.
In the bearing structure of the rotor tail end of a gas turbine, since the seal portions provided on opposite sides of the bearing pad are made longer in the axial direction than that of the conventional seal portions, the lubricant supplied to a space between the shaft portion of the rotor tail end and the bearing pad can be spread over a broader surface area of the shaft portion in the axial direction. Consequently, a broader surface area of the shaft portion in the axial direction can be cooled by the lubricant, so that it is possible to maintain the surface temperature of the portion of the shaft portion that is opposed to the bearing pad, at a temperature below a predetermined value. Consequently, it is possible to restrict the thermal deformation, and particularly, the thermal expansion of the shaft portion in the radial direction, at the outer surface portion of the shaft portion that is opposed to the bearing pad, within an allowable limit.
According to another aspect of the present invention, there is provided a shaft structure of a rotor tail end of a gas turbine in which a steam passage for supplying and recovering a steam for cooling rotor blades of the gas turbine extends along a center axis of the rotor assembly of the gas turbine, wherein said rotor tail end is provided therein with a center hole coaxial to the center axis of the steam passage; a thermal sleeve is provided between the steam passage and the inner surface of the center hole of the rotor tail end; a thermal insulation gas layer is formed between the inner surface of the center hole of the rotor tail end and the thermal sleeve; and cooling air is circulated from the outside into the thermal insulation gas layer to enhance the cooling effect of the rotor.
According to another embodiment of the present invention, the thermal sleeve is in the form of a substantially circular cylinder which is welded at its one end to an end disk of the gas turbine and is welded at the other end to a shaft portion of the rotor tail end through a bellows which reduces a thermal stress due to a thermal expansion of the thermal sleeve.
According to another aspect of the present invention, there is provided a shaft structure of a rotor tail end of a gas turbine in which a steam passage for supplying and recovering a steam for cooling rotor blades of the gas turbine extends along a center axis of the rotor assembly of the gas turbine, wherein the rotor tail end is provided therein with a center hole coaxial to the center axis of the steam passage; a steam pipe is provided in the center hole of the rotor tail end; a thermal insulation gas layer is formed between the inner surface of the center hole of the rotor tail end and the steam pipe; and the steam pipe is connected to a stationary steam pipe through seal fins (labyrinth seal), so that the extension of the steam pipe due to the thermal expansion can be absorbed by the sliding movement of the seal fins.
These and other objects, features, and advantages of the present invention will be more apparent from in light of the detailed description of exemplary embodiments thereof as illustrated by the drawings.